Wire size calculation of PV system

Recently a solar PV systems sales outfit sent me a drawing for a 1500w PV system, comprised of 2 parallel strings of 3 250w panels in series going to a combiner box. Each string developed 105v at just under 7.4a each, for a total combined amperage of 14.7a. Section 690.8 states that the sum of the amperage of all modules in parallel times 125% be used to calculate the conductor size. 14.7 X 1.25 = 18.375a. To be safe I would use #10 THHN in the conduit to carry the current the 50 ft to the charge controller. The sales outfit claims that each collector is a module at 7.4a, and all 6 taken in parallel develope roughly 44a. 44a X 125% = 55a which requires #6 wire to the charge controller. In this case, what does section 690.8 require, #10 or #6 to the controller? Remember that the actual output of the array, as wired is 14.7a. Isn't that the value times 125% used to calculate the wire size?

You're correct David. There may need to be additional ampacity adjustments for conditions of use, but you're on the right track. The sales outfit seems to lack a basic understanding of Ohms law. Best of luck.